An automated external defibrillator (AED) is a device that diagnoses and treats certain types of life-threatening cardiac arrhythmias. The AED may use defibrillation (i.e., applying an electrical current) to stop the arrhythmia and direct the heart to re-establish a normal rhythm. AEDs are designed to be used in public environments and by non-medical operators. AEDs may provide audio prompts and/or visual prompts to guide users. For example, the AED may direct a user to position sensor pads in specific locations on the patient, and the AED may automatically diagnose the heart arrhythmia based on readings collected from the sensor pads. If the AED determines that defibrillation is needed, the AED may direct the user on how to correctly apply the defibrillation to the patient.